Water pipes refer to pipes, such as pipes for waterworks, drainage, fire protection, and the like, through which water is transferred.
Typical water pipes are generally prepared using steel pipes. However, since water flows through the water pipe, a steel-based water pipe inevitably suffers from corrosion of an inner surface thereof.
To solve such a problem, highly corrosion-resistant materials, such as aluminum, stainless steel, and the like, are often used for water pipes but have problems in terms of high cost and low strength. Further, a pipe coated with a highly corrosion resistant material on an inner surface thereof can be used for water pipes but suffers from easy separation of the coated material according to use conditions.
Thus, in consideration of manufacturing cost, corrosion resistance, outer strength, and the like, there is a need for a double water pipe, in which an inner side of the water pipe is coated with a corrosion resistant material such as aluminum, stainless steel, or the like, and an outer side of the water pipe is formed of typical steel.
Generally, such a double water pipe may be manufactured using a bonding agent filling process or a shrink fitting process.
In the bonding agent filling process, a bonding agent or synthetic resin is provided to a space between the inner pipe and the outer pipe to couple the inner pipe to the outer pipe. This process has a problem in that performance of coupling the inner pipe and the outer pipe is deteriorated due to chemical variation of the bonding agent or synthetic resin according to temperature or other conditions.
Further, the shrink fitting process refers to a method of heating or cooling the inner pipe or the outer pipe. In the method of manufacturing a double pipe via the shrink fitting process, expensive heat treatment equipment is used and a long double pipe cannot be manufactured to have a uniform bonding surface only through heat treatment.
Therefore, there is a need for a technique for manufacturing a water pipe of a double-pipe structure while providing excellent coupling performance and ensuring uniform bonding at a bonded interface.